A method for calculating cell edge leakage in a semiconductor device comprising performing a device leakage simulation to obtain leakage information for different cell edge conditions and providing attributes associated with cell edges in the semiconductor device. The method further comprises performing an analysis to identify cell abutment cases present in the semiconductor device and calculating the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation.
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1. A method for calculating cell edge leakage in a semiconductor device comprising:
performing a device leakage simulation to obtain leakage information for different cell edge conditions;
providing attributes associated with cell edges in the semiconductor device;
performing an analysis to identify cell abutment cases present in the semiconductor device; and
calculating the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation;
wherein the cell abutment cases comprise a source-source boundary, a source-drain boundary, and a drain-drain boundary.
10. A system for calculating cell edge leakage in a semiconductor device comprising:
a library containing device leakage simulation results related to leakage information for different cell edge conditions;
an input for obtaining attributes associated with cell edges in the semiconductor device;
a processor configured to perform an analysis to identify cell abutment cases present in the semiconductor device; and calculate the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation; and
an output for outputting the cell edge leakage in the semiconductor device;
wherein the cell abutment cases comprise a source-source boundary, a source-drain boundary, and a drain-drain boundary.
17. A method for designing a semiconductor device comprising:
calculating cell edge leakage of the semiconductor device to obtain a more accurate assessment of the leakage in the semiconductor device than relying on a worst case scenario; and
designing the layout of the semiconductor device based at least in part on the calculated cell edge leakage;
wherein calculating cell edge leakage of the semiconductor device comprises:
performing a device leakage simulation to obtain leakage information for different cell edge conditions;
providing attributes associated with cell edges in the semiconductor device;
performing an analysis to identify cell abutment cases present in the semiconductor device; and
calculating the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulations;
wherein the cell abutment cases comprise a source-source boundary, a source-drain boundary, and a drain-drain boundary.
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wherein the Ltotal_edge_leakage is the cell edge leakage in the semiconductor device; Ledge_device is the leakage information associated with the cell edge, P is a state probability of the cell abutment cases for a given abutment case k, and A is the placement for a given abutment case k.
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This relates to semiconductor devices and more particularly to systems and methods for calculating edge leakage between adjacent semiconductor cells.
Semiconductor devices may include several transistor cells arranged in a predefined pattern. For example, in the case of FET (field effect transistor) devices, several source/drain pairs may be fabricated on a substrate and a corresponding gate electrode may be formed over the source/drain pair. In operation, adjacent cells may experience a leakage current at the edge of cell. As a result, adjacent cells may be separated to reduce the overall effect of leakage within the semiconductor device. However, separating adjacent cells results in an increase in the design area of the semiconductor device.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Semiconductor devices may include several transistor cells arranged in a predefined pattern. For example, in the case of FET (field effect transistor) devices, several source/drain pairs may be fabricated on a substrate and a corresponding gate electrode may be formed over the source/drain pair. In operation, adjacent cells may experience a leakage at the edge of cell. One type of semiconductor device that experiences leakage is a continuous oxide diffusion (CNOD) semiconductor device. In a CNOD semiconductor device, adjacent cells experience the typical leakage currents associated with other types of semiconductor devices as well as an additional leakage at the edges of the cells because of the continuous nature of the oxide diffusion region. In a CNOD semiconductor device, the source and drain for multiple semiconductor cells are formed in a continuous oxide diffusion substrate. As a result of this structure, the separation between adjacent cells is accomplished by doping the oxide diffusion layer to form a filler region. In some instances, there may not be any physical separation between adjacent cells. The additional leakage experienced by the CNOD semiconductor device varies depending on the cell boundary conditions (e.g., whether the edge of the cell is a source-source boundary, a source-drain boundary, or a drain-drain boundary, different filler regions, and/or different voltage thresholds).
Although
Because these different attributes of the transistors and cells (e.g., abutment type, voltage thresholds, MOS type, etc.) contribute to differences in the amount of leakage (e.g., additional leakage) at different boundaries between adjacent cells, simply assuming a worst case scenario for leakage during the design of a semiconductor device, may be undesirable and in some cases inaccurate. In some embodiments, it may be desirable to more accurately determine the edge leakage of the device by analyzing the actual device.
The Threshold Voltages 202, CNOD design 204, and Threshold Voltage Design Flow 206 may collectively provide relevant information about the semiconductor device of interest. For example, the Threshold Voltages 202 information may provide information about the different cells and their corresponding threshold voltages (SVT, LVT, uLVT, etc.). The CNOD design information 204 and the Threshold Voltages Design Flow information 206 may provide information about different attributes of the cell. For example, the attributes may include the type of cell (e.g., PMOS or NMOS), the probability that the cell contains a logically high voltage (e.g., logical 1), the probability that the cell contains a logically low voltage (e.g., logical 0), the position of the source and drain, etc. In some embodiments, the CNOD design information 204 may provide information about the cell placement in the design. The cell placement may include the cell location and orientation for abutment cases analysis processor 210 to know the cell boundary conditions. In some embodiments, the Threshold Voltages Design Flow information 206 may provide some factors to decrease/increase leakage of the device (e.g., whole design leakage). In some embodiments, it may be time consuming to calculate all of the abutment conditions for leakage. Accordingly, in some embodiments, the processor 210 may use scaling factors (or a similar construct) to represent the additional leakage of design.
Utilizing the library information and the attributes of the actual semiconductor device of interest, the abutment case analysis processor 210 may be configured to perform a design abutment analysis to identify the various abutment cases present in the semiconductor design of interest and calculate the probability of particular states for the various abutment cases. Then this information may be combined with the leakage information obtained from the library to output a calculation of the CNOD design edge leakage 212. The abutment case analysis processor 210 may also be configured to communicate information to the layout and/or fabrication module 214 to enable the layout and/or fabrication module 214 to create a layout and/or fabricate the semiconductor device or modify the layout of an existing semiconductor device.
In some embodiments, the total edge leakage of the semiconductor device may be determined by the following formula:
In the equation above, Ltotal_edge_leakage is the total leakage of the semiconductor device; Ledge_device is the device leakage of the cell edge as determined by the simulation/library discussed above, k corresponds to the various abutment cases—drain-drain, drain-source, and source-source (DD, DS, SS), Pk is the state probability (e.g., the probability that a particular boundary state exists) as determined based on the design of the semiconductor device for a given abutment case k, and Ak is the placement for the particular abutment cases k. This total edge leakage determination is described in further detail below in the example use case walkthrough of
In some embodiments, the leakage obtained using the methods and systems described herein may be used to reduce the leakage impact of the design by about 40% enabling the design of the semiconductor device to be smaller (e.g., about 5-7% smaller). In some embodiments, a particular design choice may be selected based at least in part on whether the leakage savings in more/less than a predetermined threshold compared to the area increase/decrease of the semiconductor device. For example, in some embodiments, an increase in the amount of leakage may be tolerated in exchange for enabling the semiconductor device to be smaller. In some embodiments, a large device may be accepted in exchange for reduced leakage. In some embodiments, this (an other) information may be used to modify an existing design of a semiconductor device. For example, the new design or design choice may be compared to an existing design choice an various relative metrics (e.g., the relative percentages discussed above) may be provided as a comparison between an existing and modified design.
Next, the table is divided into two sections—a PMOS section (610, 612, 614) and an NMOS section (616, 618, 620). As discussed above, the MOS type (PMOS or NMOS may also be a relevant cell attribute. The same information is obtained/calculated for both the PMOS and the NMOS devices. In columns 610 and 616, the device leakage (Ledge_device) is provided. As discussed above, this information may be obtained by performing device leakage simulating. In columns 612 and 618, abutment probabilities are provided. In this case, the numerical value in this column corresponds to the sum of all the probabilities in the whole design. For example, the probability of each abutment case in the design may be calculated for all of the adjoining cells and then the boundaries with the identified MOS type, adjoining cells and abutment cases may be summed together. In columns 614 and 620, the product of the device leakage and abutment are provided for each boundary. The values in column 614 are summed to obtain the total PMOS edge leakage 622 and the values in column 620 are summed to obtain the total NMOS edge leakage 624. Edge leakage values 622 and 624 are summed to obtain the total leakage value of the semiconductor device 626.
For example, looking at the first row of the table, the cell edge is formed by two SVT transistors (602, 604). The drains of both transistors are aligned at the edge (606) and there is no filler (608). The leakage simulation has identified that device leakage in this condition to be 5.4E-06 (610). Column 612 indicates that the sum of the state probabilities for this condition is 7115.8 (i.e., the state probability for a cell edge meeting this condition multiplied with the total number of cell edges meeting the defined conditions). The device leakage 610 and the abutment 612 are multiplied to obtain the leakage attributable to all of the cell edges in the semiconductor device meeting the defined conditions (i.e., SVT-SVT, DD, Filler-0, PMOS) 614.
As further indicated in
Some embodiments described herein may include a method for calculating cell edge leakage in a semiconductor device comprising performing a device leakage simulation to obtain leakage information for different cell edge conditions and providing attributes associated with cell edges in the semiconductor device. The method further comprises performing an analysis to identify cell abutment cases present in the semiconductor device and calculating the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation.
Some embodiments described herein may include a system for calculating cell edge leakage in a semiconductor device comprising a library containing device leakage simulation results related to leakage information for different cell edge conditions and an input for obtaining attributes associated with cell edges in the semiconductor device. The system may further include a processor configured to perform an analysis to identify cell abutment cases present in the semiconductor device; and calculate the leakage of the semiconductor device based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation. An output may be provided for outputting the cell edge leakage in the semiconductor device.
Some embodiments described herein may include a method for reducing the layout size of a semiconductor device comprising calculating cell edge leakage of the semiconductor device to obtain a more accurate assessment of the leakage in the semiconductor device than relying on a worst case scenario and designing the layout of the semiconductor device based at least in part on the calculated cell edge leakage. The step of calculating cell edge leakage of the semiconductor device may comprise performing a device leakage simulation to obtain leakage information for different cell edge conditions, providing attributes associated with cell edges in the semiconductor device, and performing an analysis to identify cell abutment cases present in the semiconductor device. The calculation of the leakage of the semiconductor device may be based at least in part on probabilities associated with the cell abutment cases and the simulated leakage values obtained from the device leakage simulation.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
Tzeng, Jiann-Tyng, Young, Charles Chew-Yuen, Sio, Kam-Tou, Peng, Shih-Wei
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